1. Field of the Invention
The present invention relates to isolated polypeptides having protease activity and isolated nucleic acid sequences encoding the proteases. The invention also relates to nucleic acid constructs, vectors, and host cells, including plant and animal cells, comprising the nucleic acid sequences, as well as methods for producing and using the proteases, in particular the use of the proteases in animal feed, and detergents.
2. Background of the Invention
In the use of proteases in animal feed (in vivo), and/or the use of such proteases for treating vegetable proteins (in vitro) it is noted that proteins are essential nutritional factors for animals and humans. Most livestock and human beings get the necessary proteins from vegetable protein sources. Important vegetable protein sources are e.g. oilseed crops, legumes and cereals.
When e.g. soybean meal is included in the feed of mono-gastric animals such as pigs and poultry, a significant proportion of the soybean meal solids is not digested efficiently (the apparent ileal protein digestibility in piglets, growing pigs and poultry such as broilers, laying hens and roosters is only around 80%).
The gastrointestinal tract of animals consists of a series of segments each representing different pH environments. In mono-gastric animals such as pigs and poultry and many fish the stomach exhibits strongly acidic pH as low as pH 1-2, while the intestine exhibit a more neutral pH in the area pH 6-7. Poultry in addition to stomach and intestine also have a crop preceding the stomach, pH in the crop is mostly determined by the feed ingested and hence typically lies in the range pH 4-6. Protein digestion by a protease may occur along the entire digestive tract, given that the protease is active and survives the conditions in the digestive tract. Hence, proteases which are highly acid stable for survival in the gastric environment and at the same time are efficiently active at broad physiological pH of the target animal are especially desirable.
Also, animal feed is often formulated in pelleted form, where steam is applied in the pelleting process. It is therefore also desireable that proteases used in animal feed are capable to remain active after exposure to steam treatment
Polypeptides Having Protease Activity
Polypeptides having protease activity, or proteases, are sometimes also designated peptidases, proteinases, peptide hydrolases, or proteolytic enzymes. Proteases may be of the exo-type that hydrolyse peptides starting at either end thereof, or of the endo-type that act internally in polypeptide chains (endopeptidases). Endopeptidases show activity on N- and C-terminally blocked peptide substrates that are relevant for the specificity of the protease in question.
The term “protease” is defined herein as an enzyme that hydrolyses peptide bonds. This definition of protease also applies to the protease-part of the terms “parent protease” and “protease variant,” as used herein. The term “protease” includes any enzyme belonging to the EC 3.4 enzyme group (including each of the thirteen subclasses thereof). The EC number refers to Enzyme Nomenclature 1992 from NC-IUBMB, Academic Press, San Diego, Calif., including supplements 1-5 published in Eur. J. Biochem. 223: 1-5 (1994); Eur. J. Biochem. 232: 1-6 (1995); Eur. J. Biochem. 237: 1-5 (1996); Eur. J. Biochem. 250: 1-6 (1997); and Eur. J. Biochem. 264: 610-650 (1999); respectively. The nomenclature is regularly supplemented and updated; see, e.g., www.chem.qmw.ac.uk/iubmb/enzyme/index.html.
The proteases of the invention and for use according to the invention are selected from the group consisting of:
(a) proteases belonging to the EC 3.4.21. enzyme group; and/or
(b) Serine proteases of the peptidase family S1, or more specifically S1A; as described in Biochem. J. 290: 205-218 (1993) and in MEROPS protease database, release, 9.4 (31 Jan. 2011) (www.merops.ac.uk). The database is described in Rawlings et al., 2010, MEROPS: the peptidase database. Nucleic Acids Res. 38: D227-D233.
More specifically the proteases of the invention are those that prefer a hydrophobic aromatic aa residue in the P1 position.
For determining whether a given protease is a Serine protease, and a family S1A protease, reference is made to the above Handbook and the principles indicated therein. Such determination can be carried out for all types of proteases, be it naturally occurring or wild-type proteases; or genetically engineered or synthetic proteases.
The peptidases of family S1 contain the catalytic triad His, Asp and Ser in that order. Mutation of any of the amino acids of the catalytic triad will result in loss of enzyme activity. The amino acids of the catalytic triad of the S1 protease 1 from Kribbella solani (SEQ ID NO: 2) and Kribbella aluminosa (SEQ ID NO: 4) are probably positions His-138, Asp-168 and Ser-250.
Protease activity can be measured using any assay, in which a substrate is employed, that includes peptide bonds relevant for the specificity of the protease in question. Assay-pH and assay-temperature are likewise to be adapted to the protease in question. Examples of assay-pH-values are pH 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12. Examples of assay-temperatures are 5, 10, 15, 20, 25, 30, 35, 37, 40, 45, 50, 55, 60, 65, 70, 80, 90, or 95° C. Examples of protease substrates are casein, such as Azurine-Crosslinked Casein (AZCL-casein), or suc-AAPF-pNA. Examples of suitable protease assays are described in the experimental part.